Classic Parts has a kit that includes that broken part. Other vendors likely have it also, that's just the first one I checked. Oh rats, I just saw it's out of stock but someone else might have it. At least you know there's a kit being made for it. Classic's p/n is 53-571.... link to page: https://www.classicparts.com/1978-91...info/53%2D571/. Pic of kit: